1. Field of the Invention
The present invention relates to a facsimile communication system for performing facsimile communication via an IP network, a facsimile apparatus, a facsimile communication method, a transmission processing method, and a reception processing method.
2. Description of the Related Art
Recently, in many cases, the communication method has been shifting toward a method utilizing an IP (Internet Protocol) as the common basis, i.e. a method of performing communication via the Internet or an intranet, using the IP.
Further, in the IP communication, data transmitted over an IP network is always in danger of being illegally viewed or tampered with. To protect data from the danger, a recent trend is to introduce encryption means using IPsec (Internet Protocol Security) which performs encryption and authentication of IP packets (see a relevant RFC).
The IPsec incorporates a key exchange function, an authentication function, and an encryption function. The key exchange function is to safely exchange information on keys necessary for authentication or encryption. The authentication function is to perform authentication of a sender of IP packets by adding a header called an AH (Authentication Header) to the IP packets to thereby prevent a malicious third party pretending to be the authorized user from sending unauthorized packets. The encryption function is to add a header called an ESP (Encapsulating Security Payload) to each IP packet to thereby encrypt the entire packet including the ESP header or only the payload of the packet. Encryption of the entire packet is called the “tunneling mode”, and encryption of only the payload as “transport mode”.
Communication using an IP has the advantage of enabling high-speed communication and reducing communication charge. Therefore, the IP communication is employed for facsimile communication, and facsimile communication using an IP (hereinafter referred to as “IP-FAX communication”) is specified in ITU-T recommendation T.38. In IP-FAX communication, as in G3 FAX communication, data is directly transmitted to a receiving end in a state communicatively connected to the receiving end (real-time communication). In this IP-FAX communication as well, data is in danger of being illegally viewed, leaked, or tampered with.
To solve this problem, there has been proposed a facsimile apparatus that performs encrypted communication only on a communication network (the Internet) (see Japanese Laid-Open Patent Publication (Kokai) No. 2002-232722). In a case where this facsimile apparatus is used for communication, first, negotiation is done between an apparatus at a transmitting end and an apparatus at a receiving end to make a decision as to whether to perform encrypted communication or non-encrypt communication. If encrypted communication is determined to be used by the negotiation, the transmitting-end apparatus encrypts data to be transmitted, by a predetermined encryption system. Then, the encrypted data is transmitted to the receiving-end apparatus via a communication network in accordance with ITU-T recommendation T.38.
On the other hand, if non-encrypt communication is selected, the transmitting-end apparatus transmits the data to the receiving-end apparatus without encrypting the same.
For example, when the data to be transmitted has high confidentiality, the transmitting-end user prefers encrypted communication. However, if the receiving-end apparatus does not support encrypted communication, the transmitting-end user and the receiving-end user decides to perform non-encrypt communication through negotiation. In this case, the data having high confidentiality is transmitted by non-encrypt communication without being encrypted, against the intention of the user who prefers encrypted communication. Therefore, there is a demand for a facsimile apparatus which is capable of selectively performing one of encrypted communication and non-encrypt communication with reliability.